Method of preparing binder layers

ABSTRACT

THIS INVENTION RELATES TO A PROCESS FOR PRODUCING A PHOTOSENSITIVE MEMBER COMPRISING CO-EVAPORATING A PHOTOCONDUCTIVE MATERIAL AND AN ORGANIC RESINUOUS BINDER AND DEPOSITING UPON A CONDUCTIVE BACKING MEMBER A THIN LAYER OF PHOTOCONDUCTIVE MATERIAL DISPERSED THROUGHOUT THE ORGANIC RESINOUS BINDER MATERIAL.

1974 J. c SCHOTTMILLER ETAL 3,738,889

METHOD OF PREPARING BINDER LAYERS Filed Dec. 9, 1970 WAT ER INLET WATER OUTLET R M E\ 1 N V l H B m w DL 0 mm m S O E T T R H m P N A m GASKET VACUUM VESSEL TO 6 HIGH VACUUM PUMP INVENTORS JOHN CHARLES SCHOTTMI LLER BY CHARLES WOOD @M i/ ATTO EV United States Patent 3,788,889 METHOD OF PREPARING BINDER LAYERS John Charles Schottmiller, Penfield, N.Y., and Charles Wood, Sycamore, Ill., assignors to Xerox Corporation, Stamford, Conn.

Continuation-impart of abandoned application Ser. No. 631,089, Apr. 14, 1967. This application Dec. 9, 1970, Ser. No. 96,398

Int. Cl. G03g 5/08 U.S. Cl. 117-201 12 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for producing a photosensitive member comprising co-evaporating a photoconductive material and an organic resinous binder and depositing upon a conductive backing member a thin layer of photoconductive material dispersed throughout the organic resinous binder material.

This application is a continuation-in-part of applicants copending application Ser. No. 631,089, filed Apr. 14, 1967, now abandoned.

BACKGROUND OF THE INVENTION In the xerographic process as described in U.S. Pat. 2,297,691 to C. F. Carlson, a base plate of relatively low electrical resistance such as metal, paper, etc. having a photoconductive insulating surface coated thereon, is electrostatically charged in the dark. The charged coating is then exposed to a light image. The charges leak off rapidly in the base plate in proportion to the intensity of light to which any given area is exposed; the charge being substantially retained in non-exposed areas. After such exposure, the coating is contacted with electrostatic marking materials in the dark. These particles adhere to the areas where the electrostatic charges remain forming a powder image corresponding to the electrostatic latent image. The powder image can then be transferred to a sheet of transfer material resulting in a positive or negative print, as the case may be, having excellent detail and quality. Alternatively, when the base plate is relatively inexpensive as in the case of paper, it may be desirable to fix the powder image directly to the plate itself.

As discussed in Carlson, photoconductive insulating coatings comprise anthracene, sulphur, or various mixtures of these materials, such as sulfur with selenium, etc., to thereby form uniform amorphous coatings on the base material. These materials have a sensitivity largely limited to the shorter wavelengths and have a further limitation of being only slightly light-sensitive. Consequently, there has been a continuing effort to produce improved photoconductive insulating materials and xerographic plates.

The discovery of the photoconductive insulating properties of highly purified vitreous selenium has resulted in this material becoming the standard in commercial xerography. The photographic speed of this material is many times that of the prior art photoconductive insulating materials. Such a plate is characterized by being capable of receiving a satisfactory electrostatic charge and selectively dissipating such a charge when exposed to a light pattern. However, vitreous selenium suifers from two serious defects: (1) its spectral response is very largely limited to the blue or near ultra-violet range; and (2) the preparation of uniform films of vitreous selenium has required highly involved and critical processes, particularly processes involving the preparation of extremely clean substrates and requiring vacuum deposition techniques. Also, vitreous selenium layers are only meta-stable in that they are readily recrystallized to inoperative crystalline form at temperatures only slightly in excess of those prevailing in conventional xerographic copying machines. These factors, together with the high cost of selenium itself has led, by commercial necessity, to the use of selenium xerographic plates only in repetitive processing cycles; that is, the selenium plate must be re-used many times in the xerographic process, so that the cost per copy of such a plate may be a reasonable small figure. Under conditions of optimum use, a vitreous selenium plate can be used to prepare 100,000 or even more copies before it deteriorates to the point of unsatisfactory image formation. Under less suitable conditions far fewer copies can be made. Because of these economical and commercial considerations, there has been a continuing effort towards developing photoconductive insulating materials other than selenium for use in the xerographic mode.

It has been proposed that various two component materials be used as photoconductive insulating layers for xerographic plates. Exemplary two component xerographic plates are those disclosed by Middleton et al. in U.S. 3,121,006 wherein particulate photoconductive materials are dispersed in an insulating organic resinous binder. The general preparation of this photoconductive binder plate comprises dispersing photoconductive insulating compound in a high electrical resistance resins binder, dissolving the resulting composition in a suitable solvent, and thereafter coating said composition on a base plate by dipping, whirling or by any other well known means. Alternatively, the binder plate can be prepared by heating a photoconductor-thermoplastic resin binder to render it plastic thereby obviating the need for a solvent. In these preparations, however, it is difiicult to obtain a uniform dispersion of particulate photoconductive material throughout the resinous binder. Use of a non-uniform dispersion to produce the xerographic plate creates zones or portions on the surface of the xerographic plate which, though capable of accepting and maintaining an electrostatic charge, are non-photoconductive and, therefore, will not dissipate the surface charge in response to impinging radiation.

In view of the state of the art, it can readily be seen that there is a need for a preparation of photoconductive binder plates which obviate the aforementioned difficulties and which additionally provides photoconductive binder plates having outstanding xerographic Properties.

OBJECTS OF THE INVENTION It is, therefore, an object of this invention to provide a method for the production of a light responsive member having high dark resistivity.

It is a further object of this invention to provide a method for the production of an improved organic resinous-binder xerographic plate.

It is a further object of this invention to provide a method for producing an organic resinous binder xerographic plate which produces copies having reduced background density.

Still a further object is to provide an improved lightresponsive member of high dark resistivity.

Still a further object of this invention is to provide an improved xerographic plate.

Still a further object of this invention is to provide an organic resinous-binder xerographic plate which produces copies having reduced background density.

The above and still further objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed disclosure of specific exemplary embodiments of the present invention.

SUMMARY OF THE INVENTION The above and still further objects may be accomplished in accordance with the present invention by simultaneously co-evaporating the photoconductive material and the organic resinous binder and depositing upon a suitable conductive backing member a thin layer of particulate photoconductive material dispersed throughout the resinous binder.

In a preferred embodiment of the present process, a resin binder material, in the form of a monomer or dimer, and a photoconductive material are heated in a vacuum evaporation chamber. When the heated vapors reach an equilibrium condition in the chamber, a conductive substrate is exposed thereby allowing the vapors to condense and deposit thereon. During deposition, the newly formed resin coating is subjected to a polymerization initiation technique which causes polymerization of the resin binder material. This combination of co-evaporation and subsequent polymerization of the binder material results in a totally'homogeneous photoconductive binder layer. Since a homogeneous layer is produced, its sensitivity is uniform over its entire applicable surface as well as throughout its its depth. Further, since a uniform layer is produced on the conductive backing, there will be a minimization of non-photoconductive areas on the photoreceptor surface which, though capable of receiving an electrostatic charge, will not dissipate such charge in response to impinging radiation. This will significantly reduce background density in developed xerographic copies.

In yet further embodiments, the present co-evaporation process can be modified by varying conditions, as well as utilizing catalytic agents for the resin binder material, to produce a photoconductive layer of varying composition. Thus, there can be produced a photoreceptor layer having a plurality of zones of different composition, each zone functioning to provide a specific result which will increase the overall effectiveness of the photoresponsive member.

The binder material which is employed in the practice of the present invention is a material which is an insulator to the extent that an electrostatic charge placed on the layer is not conducted by the binder at a rate to prevent the formation and retention of an electrostatic latent image or charge thereon. The binder material is adhered tightly to the supporting substrate and provides an efiicient dispersing medium for the photoconductive powder. The binder material should be easily evaporated and should have a sufiicient vapor pressure, at the ambient conditions existing during deposition, whereby substantial deposition rates can be obtained. The binder material should not decompose at elevated temperatures either into gaseous materials or other materials which are incapable of polymerizing or providing the insulating material having the desired physical characteristics for the deposited photoreceptor layer. Satisfactory binder materials include polystyrene; silicone resins such as DC-704, DC-801, DC-804 and DC-996 all maufactured by the Dow Corning Company and SR-82 manufactured by the General Electric Company; vinyl polymers and copolymers such as polyvinyl acetate; acrylic and methacrylic ester polymers such as methyl acrylate and methyl methacrylate; epoxy resins produced from the condensation of epichlorohydrin with -bisphenol-A; parylene polymers, thermoplastic film polymers based on para-xylylene; etc. In addition, mixtures of such resins with each other or with plasticizers so as to improve adhesion, flexibility, blocking, etc. of the coatings may be used.

The photoconductive materials suitable for use in the present invention are characterized by having electrons in the non-conductive energy level activable by illumination to a different energy level whereby an electric charge is free to migrate under an applied field, the composite resistivity of the binder and the photoconductive material in the layer being capable of retaining surface electrostatic charge in the absence of light for a period of time sufiicient for the formation and development of an electrostatic latent image. A more complete discussion of applicable materialsis given in Middleton et al. US. 3,121,006. Portions of the Middleton patent which are necessary to the complete understanding of the present invention are incorporated herein by reference. In addition to the requirements set forth in the Middleton et a1. patent, the photoconductive materials should be capable of being transformed to the vaporous state under conditions which are suitable for deposition of the binder material. At these conditions, the photoconductive material should not decompose into deleterious by-products, that is, materials, etc., which will not recombine during deposition to give a photoconductive material. Additionally, the vapor pressure of the material should be such that sufiicient material can be incorporated in the photoconductive layer during deposition. Any and all photoconductors which are capable of being vapor deposited are within the purview of the instant invention. Particularly satisfactory photoconductive materials are inorganic materials such as selenium, cadmium sulfide, cadmium selenide, zinc oxide, zinc sulfide, lead oxide, antimony trisulfide, arsenic triselenide, gallium sulfide, gallium phosphide, gallium triselenide, gallium arsenide, and organic photoconductors such as phthalocyanines and quinacridones.

A conductive backing is usually required for xerographic plates and metal forms the most suitable material. However, a high conductivity is not required and almost any structurally satisfactory material which is more conductive than the photosensitive layer can be used. Materials having electrical resistivities of about 10 ohmcentimeter are generally satisfactory for the base plate of this invention although it is more desirable to use materials of less than about 10 ohm-centimeter. Any gross surface irregularities, i.e., burns, tool marks, etc., should be removed from the base plate by grinding or polishing although it is unnecessary to polish the plate to a mirrorlike finish. The conductive backing surface is cleaned before coating with the photosensitive layer in order to remove grease, dirt, and other impurities which might prevent film adherence of the coating to the base plate. Suitable backing materials include aluminum, stainless steel, nickel, chromium, zinc, steel, glass having a conductive coating thereon as of tin oxide (NESA glass) or aluminum, conductive plastic, conductively coated paper, etc. It should be understood that the backing members may be in the form of a fiat plate, a cylinder, flexible sheet, or other member having a surface suitable for receiving the photosensitive layer for use in the xerographic process.

Any suitable method can be utilized to evaporate the organic resinous binder material whereby solid or liquid binder material is transformed into the vaporous state. The particular method chosen will depend upon the particular binder material and, to a lesser extent, the photoconductive material being utilized. The binder material is supplied in a form which can easily be evaporated and which will provide deposition rates so that the thin films of sufficient thickness can be obtained within a reasonable amount of time. In a preferred embodiment of the instant invention, the binder material will be provided in a low molecular weight form, i.e., monomeric or dimeric form, for evaporation. Although more fully polymerized forms can be utilized, as the molecular weight of a polymer increases it generally becomes more difficult to evaporate and, therefore, a molecular weight is rapidly reached above which the particular material cannot feasibly be used.

The binder material is evaporated under low pressure or vacuum conditions with the vapor being drawn into the vicinity of a conducting substrate held at a temperature which induces deposition in the form of a polymerized binder. In general, it is known that the rate of deposition varies inversely with the substrate temperature. Thus, controlling the substrate temperature is one method by which the rate of deposition can be controlled. Normally the substrate upon which the film deposits is held at a temperature which is cooler than the temperature of the binder material source. The substrate may be below room temperature, at room temperature or even heated above room temperature depending upon the particular materials being utilized and the particular rate of deposition desired. If necessary, polymerization initiators can be provided within the deposition chamber to induce and/ or control the rate of polymerization. Suitable initiators include ultra-violet radiation, electron bombardment, glow discharge means, etc.

Plural sources can be provided if the polymerized binder material is the reaction product of two or more components, as in the case of epoxy resins. Further, other materials, such as free-radical generators, catalytic agents, etc., can be injected into the vacuum deposition chamber or evaporated from a suitable source if needed to produce the desired photoresponsive layer.

The photoconductive materials are held in one or more sources separate from the organic resinous binder material and subjected to conditions which will volatilize the material at a rate to provide sufiicient concentration in the deposited layer. Generally, the photoconductive material sources(s) will be in the same chamber as the organic resinous binder source, and, therefore, each will be sub jected to the same ambient conditions. However, each material can be evaporated in a separate zone, each having different ambient conditions, with only the vapors being conducted to the substrate zone for deposition. This latter technique is especially useful where the conditions required to evaporate sufficient quantities of one of the materials would have a deleterious effect on other materials present.

The rate of deposition is limited only by the rates of evaporation of the respective materials at ambient conditions and by the rate of polymerization of the binder material. The ratio of deposition of photoconductive insulating material to organic resinous binder material must be carefully maintained so that sufficient photoconductive material is trapped throughout the photosensitive layer as it is deposited upon the conductive backing. While rates of about 0.1 to about 20 microns per hour are obtainable, it is contemplated that under appropriate conditions with suitable apparatus any desired rate of deposition may be maintained. The advantageous results set forth in this application are not entirely dependent, however, upon an optimum rate of deposition; as long as the desired photosensitive layer is deposited upon the conductive backing, it should be understood that such members and the coevaporation processes used to obtain such members, are within the scope of this invention regardless of the rate of deposition of the photosensitive layer.

BRIEF DESCRIPTION OF THE DRAWING As previously indicated, in one of the preferred embodiments there is deposited upon a conductive backing a photoresponsive layer having the photoconductive insulating material homogeneously dispersed throughout the organic resinous binder material. An apparatus for producing such a layer is shown in the accompanying figure.

Referring to the figure there is seen an illustrative apparatus which can be used in preparing the improved organic resinous xerographic plates of the present invention. A clean conductive plate 1 is attached to a temperature controlled platen 2 a fixed distance from an organic resinous binder source 3. The temperature of the plate may be controlled in any suitable manner, such as by the passage of water through a suitable conduit 8 in the platen, etc. The plate temperature is maintained at a level which promotes continuous deposition of photoconductive material dispersed throughout the organic resinous binder. The source 3 holding the purified organic resinous binder is placed in the bottom of the deposition vessel and is temperature controlled whereby sufiicient amounts of the resinous binder can be transformed into the vaporous phase. A plurality of temperature controlled sources 4 each holding a quantity of photoconductive material are placed intermediate the resinous binder source 3 and the conductive backing 1. The sources 4 are supported by any suitable movable means 5 for movement towards or away from the conductive substrate. A vacuum is drawn on the vessel by means of a high vacuum pump (not shown) connected to the deposition vessel by conduit 6.

The organic resinous binder source is maintained at a temperature sufficient to provide substantial deposition of the binder material on the conductive backing. At the other extreme, the source should not be maintained at a temperature which provides (1) too great a rate of deposition so that the photoconductive material is not properly dispersed throughout the deposited layer or (2) insufficient photoconductive material is trapped in the deposited layer. The temperature at which the source is held is dependent upon the particular material being utilized as well as, to a lesser extent, the temperature requirements for the photoconductive material. The photoconductive material sources are held at a temperature whereby the photoconductive material is transformed into the vapor state in an amount sufficient to provide proper dispersion of that material throughout the deposited organic resinous binder. The temperature of these sources will also depend upon the particular material being evaporated (as well as the particular organic resinous binder being utilized). The selection of appropriate temperatures is, of course, dependent upon many interrelated factors and it should be understood that no definite range can be given for all the combinations of materials which can be used in the practice of this invention. Exact temperatures and deposition rates can be determined by routine experimentation once the particular materials have been chosen.

In the instance where monomeric or dimeric resinous materials are being co-evaporated with photoconductive materials, the heating temperature of these materials will range from about 50 C. to C. In addition, the pressure in the vacuum chamber is preferably maintained at from 1 to 5X10- mm. Hg and the substrate preferably maintained at a temperature of from about 15 C. to 30 C. during deposition.

Using the apparatus as disclosed in the figure to produce a homogeneous layer, the organic resinous binder and the photoconductive material are placed in separate sources in the high vacuum vessel and are heated to volatilize their contents at a desired deposition ratio. When a steady state equilibrium is reached, the shutter separating the sources from the conductive member is removed and the evaporation is permitted to continue until the desired depth of photosensitive layer is deposited upon the conductive substrate. The shutter is then reinserted between the binder material and the photoconductive material sources and the conductive backing to prevent further deposition, the heating units are turned oif and the entire apparatus cooled to room temperature.

In further embodiments, deposition is conducted under conditions which cause varying amounts of photoconductive material to be trapped 'within the deposited photosensitive layer. This can be achieved by using nonequilibrium conditions or by modifying the ambient conditions throughout the deposition process. Further, other photoconductive materials can be added to the deposition vessel at the appropriate time to produce layers in the photosensitive layer of different composition. Interfacial layers of pure binder material can be deposited if desired. This technique of modifying ambient conditions or materials being deposited is especially useful when it is desired to produce a photosensitive device having layers or zones of varying concentration or composition.

The practice of the present invention is not limited to the use of the apparatus as shown in the accompanying figure. Other means may be provided to bring an atmosphere of photoconductive material and organic resinous binder to the vicinity of the conductive substrate and have a photosensitive layer deposited thereon and it should be clearly understood that the disclosed apparatus merely represents one system for depositing the desired photosensitive layer. Continuous feed apparatus can be provided to more fully automate the deposition apparatus and to ensure appropriate conditions during deposition. Means can be provided whereby the materials to be deposited are sprayed into the deposition chamber rather than being evaporated from a source as shown in the figure. Other modifications can be made as will be apparent to those skilled in the art and other apparatus can be designed to achieve the same result.

The xerographic member of the present invention may be used as the photosensitive member in any of the regular xerographic processes. In general, the member is electrically charged to a potential of the order of about 100 to 800 volts by any method well known in the art. The charged member is then exposed to a light image whereby there is a selective dissipation of the electrostatic charge resulting in an electrostatic latent image. This latent image can be developed, i.e., made visible, by treatment with an electroscopic marking material and, optionally, the developed image can be transferred to a support member to yield a xerographic print. Modifications and variations of this process need not be considered as they are well known to those skilled in this art and any and all of such modifications and variations may be used to provide high quality xerographic prints.

DESCRIPTION OF SPECIFIC EMBODIMENTS The following examples are given to enable those skilled in the art to more clearly understand and practice the invention. They should be considered not as a limitation upon the scope of the invention but merely as being illustrative thereof.

In the following examples, the more important parameter is the rate of deposition of the photosensitive layer upon the conductive substrate. This parameter is dependent upon many interrelated factors, including the temperature and surface area of the material sources, ambient conditions, etc.; accordingly, the initial conditions have been determined and specified and, rather than continually monitor subsequent changes in the ambient conditions, such as the temperature changes of the sources, the rate of deposition is maintained substantially constant by varying the source temperatures. The rates of deposition are measured and controlled, for example, with a deposit rate control system such as the Sloan Instrument Corporation (Santa Barbara, Calif.) DTM2 unit in conjunction with a DRC unit. The thickness of a deposit on a vibrating rod situated between the conductive substrate and the sources varies the frequency of vibration. This is converted into an electrical signal and transmitted to the DRC unit from the DTM-Z unit. This input signal is compared with a reference signal and, as needed, more or less power is added to the respective sources. Thus, accurate control of the deposition rate is maintained even though actual temperature conditions, etc., are never measured.

EXAMPLE I Ten grams Eccomold L-28 epoxy resin (Emerson and Cummings, Inc.) is placed in a resistance heated copper boat with a surface area of 8.25 cm. and heated to 118 C. to establish a deposition rate of 600 A. per minute for the epoxy resin. Twenty-five grams of selenium is placed in a quartz crucible with a surface area of 5.75 cm. contained in a wire-wound resistance furnace and heated to 250 C. to establish a deposition rate of 2600 A. per minute. Ambient pressure in the vacuum vessel is approximately 5 10- mm. Hg. A tin oxide coated glass substrate is supported 10 inches above the sources and maintained at a temperature of 25 C. The substrate is shuttered until the desired evaporation rates are established after which the movable shutter is opened and deposition permitted to occur. During deposition an electron beam With an accelerating voltage of 1200 volts and a current density of 1.5 ma./cm. is swept across the substrate to cause polymerization of the epoxy resin as it deposited. After 30 minutes, the shutter is reinserted between the sources and the substrate. A 9.6 micron thick photoconductive film is obtained on the substrate. The plate so prepared is tested in the xerographic process utilizing a commercial charging-and exposure apparatus obtained from Xerox Corporation, Rochester, New York under the tradename Xerox Copier Model D. The resulting electrostatic image formed on the plate is made visible by cascading a mixture of toner and carrier as described in US. 2,618,552. Acceptable xerographic prints are obtained.

EXAMPLE II Example I is repeated except a 20% arsenic-selenium alloy is used in place of the selenium, the quartz crucible is heated to 360 C., and a flexible copper substrate is used in place of the tin oxide coated glass. Acceptable xerographic prints are obtained.

EXAMPLE III Example I is repeated except that cadmium sulfide is used in place of the selenium and is placed in a molybdenum boat for evaporation. The boat is heated to 800 C. and the substrate is held at 70 C. Acceptable xerographic prints are obtained.

EXAMPLE IV Example I is repeated except gallium arsenide is used in place of the selenium. The gallium arsenide granules are fed from a steel hopper down a vibrating shoot to a tungsten boat maintained at 1600 C. The gallium arsenide is flash evaporated and the deposition rate adjust to 2600 A. per minute. Acceptable xerographic prints are obtained.

EXAMPLE V Example IV is repeated except gallium phosphide is substituted for the gallium arsenide. Once again, acceptable xerographic prints are obtained.

EXAMPLE VI Example I is repeated except a DC-996 silicone resin (Dow Corning Corporation) is substituted for the epoxy resin and cadmium sulfide is substituted for the selenium. The substrate is held at 70 C. and the cadmium sulfide is placed in a molybdenum boat and heated as in Example III. Acceptable xerographic prints are obtained.

EXAMPLE VII Example I is repeated except methyl methacrylate is substituted for the epoxy resin and ultra-violet radiation is substituted for the electron bombardment. The methyl methacrylate is injected into the vacuum vessel since its vapor pressure is too high to permit the presence of a liquid or solid phase in the vacuum system. The pressure of the methyl methacrylate is maintained at a constant pressure of 15 mm. Hg during deposition. Nitro-methane is also injected into the vacuum vessel and maintained at a pressure substantially equal to that of the methyl methacrylate. During deposition the substrate is held at 25 C. and illuminated with ultra-violet light of about 2600 A. wavelength to induce polymerization. The selenium source is held at C. Deposition continues for three hours whereafter a 9 micron thick photoconductor film is obtained. Development proceeds in accordance with Example I and acceptable xerographic prints are obtained.

EXAMPLES VIII-IX Example VII is repeated substituting vinyl acetate and methyl acrylate for the methyl methacrylate. Acceptable xerographic prints are obtained.

. 9 EXAMPLES X-XIV Examples I-V are repeated using powdered polyethylene in place of the epoxy resin and omitting the electron bombardment. Evaporation is carried out from a small nickel boat held at 290 C. The powdered polyethylene is fed down a chute into the boat and flash evaporated. In all cases, acceptable xerographic prints are obtained.

EXAMPLE XV Example H is repeated except that before deposition of the photosensitive layer a substantially pure epoxy interfacial layer is vacuum deposited. A deposition rate of 2600 A. per minute is established as in Example II and the copper substrate coated for minutes with the substantially pure epoxy interface. The substrate is shuttered until the selenium alloy is brought to the desired evaporation rate whereupon the shutter is removed and deposition continues as in Example H. The unit can be flexed without adverse cracking or flaking of the photosensitive layer. Acceptable xerographic prints are obtained.

While the invention has been described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the true spirits and scope of the invention. Further, provided the advantageous results of this invention are not adversely afiected, additional operations may be performed to achieve the herein disclosed results or, in certain circumstances, certain operations may be deleted as will be apparent to those skilled in the art. All such conditions, deletions, modifications, etc., are considered to be within the scope of the present invention.

What is claimed is:

1. The process of producing a photosensitive member comprising the steps of:

(a) co-evaporating a photoconductive material and a low molecular weight organic resinous binder under vacuum conditions;

(b) continuing said evaporation until a steady state equilibrium is established;

(c) depositing the vaporized material upon a conductive backing to form a thin layer of photoconductive material dispersed throughout said resinous binder material; and

(d) subjecting said deposited layer to a polymerization initiator to induce polymerization of the resinous binder.

2. The process of claim 1 wherein the co-evaporation 10 rates of the two materials are changed during deposition to form a photoconductive binder layer of varying composition.

3. The process of claim 1 wherein the initiator is ultraviolet radiation.

4. The process of claim 1 wherein the initiator is electron bombardment.

5. The process of claim 1 wherein the low molecular weight binder material is a monomer.

6. The process of claim 1 wherein the low molecular weight binder material is a dimer.

7. The process of claim 1 wherein the co-evaporation is carried out under vacuum conditions of from about 1 to 5X10 mm. of Hg.

8. The process of claim 1 wherein the co-evaporation is carried out by heating the low molecular weight resinous binder material at temperatures of from about C. to C.

9. The process of claim 1 wherein the deposition is carried out on a conductive backing maintained at a temperature of from about 15 C. to 30 C.

10. An electrostatic element prepared by the process of claim 1.

11. The process of claim 1 wherein the photoconductive material is selected from the group of inorganic photoconductors consisting of selenium, cadmium sulfide, cadmium selenide, zinc oxide, zinc sulfide, lead oxide, antimony trisulfide, arsenic triselenide, gallium sulfide, gallium phosphide, gallium triselenide and gallium arsenide.

12. The process of claim 1 wherein the photoconductive material is selected from the group of organic photoconductors consisting of phthalocyanines and quinacridones.

References Cited UNITED STATES PATENTS 3,121,006 2/1964 Middleton et al 96-15 3,489,560 1/1970 Joseph 96--1.5 3,498,835 3/1970 Chiang et a1. 117106 R 3,374,111 3/1968 Brennemann 117106 R 3,598,644 8/1971 Guffe et al. 117106 R 3,625,744 12/1971 June et a1. 117106 R 3,301,707 1/1967 Loeb et a1 117106 R X RALPH S. KENDALL, Primary Examiner US. Cl. X.R. 

